This invention relates to an instrument for identification of a color deficiency, for example, in a clinical environment. The instrument further identifies the nature of the color deficiency as well as the degree of its severity.
The instrument utilizes a color mixing technique wherein the patient attempts to match the fixed color of one half of a bi-partite field with the other half. This second half includes capacity for varying of hue by mixing together two colors in subjectively appropriate proportions.
The principle of the color anomaloscope finds its premise in the latter of two of Grassman's three laws:
2. If, of a two-component mixture, one component is steadily changed (while the other component is maintained constant), the color of the mixture steadily changes.
3. Lights of the same color (that is, of the same dominant wavelength, same luminance, and the same purity) produce identical effects in mixtures, regardless of their spectral composition.
Further reference to the 1931 CIE Chromaticity Diagram (a standard reference in the art) illustrates that any spectral color between 540 and 700 nm can be matched by a combination of appropriate proportions of the extremes of this range. The literature of the art shows that the proportions of the mixture in any color matching attempt, within the range, are the same for any normal observer. Those individuals which are deficient in color vision may be readily identified by observation of his variation from the norm.
The two types of color deficiencies which are frequently encountered in the human are deficiency of either the protans, or the deutans. The deficiency of protans will cause an individual to exhibit a deficiency of red-response, while the deficiency of deutans is evidenced in a sub-normal green-response. Each type of anomaly may range in severity from the characteristic of anomalous trichromatism to the more severe condition of severe dichromatism. An individual having the former deficiency demonstrates a three color response, however, either depressed in the green or red response and/or green or red wavelength limited. In the severe condition of dichromatism, the response to red or green is lacking.
The conditions of tritanism, or blue-blindness and the condition of monochromatism or total color-blindness, are so rare that the inclusion in a color anomaloscope of the ability to diagnose such a condition is not necessary. Rather, such inclusion would cause a clinical instrument to be overly complicated and expensive for normal commercial application since such extreme conditions are detectable by other suitable tests.
Prior art color anomaloscopes have employed incandescent sources, utilizing the likes of glass, gelatin or interference filters to develop luminescence of known spectral color. Monochromators and gas discharge tubes have also been employed as sources for such instruments. Unfortunately, such practical considerations as high cost, difficulty of control, extensive maintenance involvement, are associated with these prior embodiments of clinical instruments; and have suppressed the utilization (commercial production and sale) of such instruments for use in clinical testing and industrial screening.
There is a real need for a wavelength accurate color response measurer which may be operated by the professional or skilled technician which commands confidence that the measurements taken are indicative of patient characteristics. The present instrument utilizing precision light-emitting diodes offers these advantages.